The present invention relates generally to actuators, and more particularly to actuators used in computer interface devices that allow the user to provide input to computer systems and allow computer systems to provide haptic feedback to the user.
A user can interact with a computer to perform functions and tasks on the computer, such as playing a game, experiencing a simulation or virtual reality environment, using a computer aided design system, operating a graphical user interface (GUI), navigate web pages, etc. Common human-computer interface devices used for such interaction include a mouse, joystick, trackball, gamepad, steering wheel, stylus, tablet, pressure-sensitive sphere, knob, or the like, that is connected to the computer system controlling the displayed environment. In some interface devices, kinesthetic force feedback and/or tactile feedback is also provided to the user, more generally known collectively herein as “haptic feedback.” These types of interface devices can provide physical sensations which are felt by the user manipulating a user manipulandum of the interface device, such as a joystick handle, mouse, wheel, etc. One or more motors or other actuators are coupled to the manipulandum and are connected to the controlling computer system. The computer controls forces on the manipulandum and/or device housing in conjunction and coordinated with displayed events and interactions by sending control signals or commands to the actuators. The computer system can thus convey physical force sensations to the user in conjunction with other supplied feedback as the user is grasping or contacting the interface device or manipulatable object of the interface device.
A problem with many types of haptic feedback interface devices, such as haptic knobs, joysticks, and other types of devices, is protecting the actuator(s) of the device from failure due to high temperatures. For example, moving-coil DC motors in haptic feedback devices are typically stalled at high currents, and so have the potential to heat up quickly. For example, a haptic feedback device may output a barrier force or other resistive force, where the user moves a manipulandum in direct opposition to the output force. This can cause excessive heat in an actuator.
A robust haptic feedback product must protect its actuators against excessive coil and magnet temperatures. This problem can be solved by mounting a thermistor directly on the motor coil and using its information to safely regulate temperature. However, it is impossible to mount a thermistor on the moving coil of a typical brushed motor. Other ways must be employed to predict and prevent destructive coil temperatures in brushed motors. More cost effective ways to prevent such temperatures in brushed motors and other types of actuators are also needed.